References IEEE P1609.4, Draft Standard for Wireless Access in Vehicular Environments (WAVE) Multi-Channel Operation—DRAFT STANDARD [1]; IEEE P1609.3—Wireless Access in Vehicular Environments (WAVE) Network Services—DRAFT STANDARD [2]; and IEEE Std. 802.11p, Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: Wireless Access in Vehicular Environments (WAVE)—DRAFT STANDARD [3] specify a wireless communications system comprised of vehicular and roadside units. The units exchange both high priority/low latency data (e.g., emergency warnings), and low priority/best effort data (e.g., map updates). They employ a series of radio channels in the 5 GHz band, one of which is designated a control/safety information (CSI) channel and others designated service channels. All devices are required to periodically tune to the CSI channel to exchange information of general interest. At other times, devices may operate on any of the service channels to exchange information of interest to a subset of the devices. These times are known as the CSI channel interval and service channel interval respectively.
Typically, Dedicated Short Range Communications (DSRC) or Wireless Access in Vehicular Environments (WAVE) systems use the CSI channel for two purposes: setting up data exchange sessions on a service channel and transmission of time-critical emergency and safety messages among vehicles and between vehicles and infrastructure. These emergency and safety messages are used for applications that involve avoiding car crashes and other emergency situations, for instance transmitting traffic signal information to a vehicle from a roadway intersection, or brake warnings from one vehicle to another. Data exchanges on service channels typically involve applications used to process payments, for instance toll collection and parking lot payments. In the DSRC embodiment, the CSI and service channel intervals may be adapted to provide maximum utilization of the appropriate channel depending on the emergency and safety messages load on the CSI channel, or the data exchange load on the service channel, so that the demands of the respective load can be most effectively accommodated based on message traffic and transmitted time critical safety messages are not missed by the receiving devices.
In [1], the CSI channel and service channel intervals are assumed to be of constant duration. This provides a guaranteed grade of service to CSI channel and service channel traffic, however, it does not accommodate adjustments to the relative allocation of channel resources if a different allocation would provide better system utilization. For example, if service channel traffic only required 10% of the channel capacity, it would still consume 50% of that resource.
U.S. Pat. No. 3,564,147 describes a Demand Assigned Multiple Access (DAMA) system, which is specifically targeted for satellite communications, while this invention is targeted for terrestrial vehicular applications. However, in DAMA, channel resources are assigned by a control station, based on pre-configured information and/or user requests. Moreover, DAMA does not employ any dynamic service channel usage monitoring and does not adjust resource allocation based on actual system utilization.
Additionally, while DAMA is a multiple access control technology assigning system resources to specific devices or services, it does not segment channel resources available to participants.
Therefore, there is a need for an improved system and method for short range communication on wireless discontinuous channels, where the resource allocation is adjusted based on actual system utilization.